1. Field of the Invention
The present invention relates to a method for redundantly linking a wide area network (WAN) node device that forms a WAN and a local area network (LAN) communication linking device that forms a LAN, to enable communication between the two, and the WAN node device.
2. Description of the Related Art
To ensure failure resilience of a network formed using Ethernet (registered trademark), a spanning tree (a spanning tree protocol) that provides redundant configuration in a network is commonly used. In the spanning tree, one path is set as an active path and remaining paths are supposed to be alternate paths at the time of failure.
For example, in the network that uses the spanning tree, when failure occurs in a port of a switch device linked to the active path, a communication control method that enables quick search of the alternate paths using a media access control (MAC) address that the switch device has learned is disclosed in Japanese Patent Application Laid-open No. 2004-297475.
A backbone link of the network connects different Ethernet networks, each formed of user lines, by connecting their nodes. Such a backbone link needs to be highly reliable and hence is often configured by synchronous optical network/synchronous digital hierarchy (SONET/SDH).
To increase the reliability when linking and relaying the Ethernet network by SONET/SDH, for a connection between the Ethernet network and the SONET/SDH, it has been suggested to introduce redundant configuration also in a connection between a SONET/SDH switch device on the SONET/SDH network side and an Ethernet switch device on the Ethernet network side.
In a conventional technology disclosed earlier, because all the switch devices are Ethernet switch devices, a MAC-address learning function is included and the MAC address can be used for searching for the alternate paths. However, when the switch devices other than the Ethernet switch devices such as the SONET/SDH switch devices, some of which do not have the MAC-address learning function, are combined, the alternate paths cannot be searched and secured.
Specifically, when the redundant configuration is introduced in the connection between the SONET/SDH switch device on the SONET/SDH side and the Ethernet switch device on the Ethernet network side, because the SONET/SDH switch devices do not include the MAC-address learning function as disclosed in the conventional technology mentioned earlier, searching for an alternate path using a key of the MAC address and securing the same is impossible.